This invention relates to an elastomeric sealing strip, which can be cured in place to provide a strong bond to a variety of surfaces, including rigid, rough surfaces such as concrete. The strip of the present invention is particularly suitable for highway seals.
Cured-in-place elastomer material offers many advantages over soft materials, such as caulks. Especially desirable properties of such elastomers are their elasticity and resistance to abrasion and weathering.
Most methods of curing an elastomer in contact with other materials, for example, concrete, are inefficient or expensive. For example, heating by radiofrequency is very expensive. Various methods of electric heating, based on the electrical resistance of properly formulated rubber itself or by imbedding electric heating wires in it, have been proposed in the past; see, for example, U.S. Pat. Nos. 3,393,257 and 2,054,000. The former method requires the use of carbon-black fillers having a steep positive temperature coefficient of resistance. The latter method suffers from the disadvantage of causing local hot-spots, which further cause unacceptable degradation of the rubber.
Joule effect heating of rubber holds the best promise because it can be both efficient and inexpensive. Heat is generated when an electric current is passed through an elastomer made conductive by blending with a conductive carbon black. Most Joule effect heating methods require additional steps as well as special precautions. Thus, heat treatment of a freshly compounded elastomer reduces its initial high resistivity to a lower, more practical value. Then, the elastomer must be mechanically constrained until cured, so that carbon particle-to-carbon particle bonds are not broken since this would increase the resistivity to an impractically high level. If a sufficient number of such particle-to-particle bonds are not formed, channeling of the electric current takes place, resulting in hot-spots and blown sections.
It, therefore, is an object of the present invention to provide an elastomeric sealing strip which will cure in a homogeneous manner and provide strong, elastic bonds.